Power transmission calculator
Motor Speed, Torque & Power Calculator
Model a DC motor torque-speed curve, power, current, efficiency, gearing, and the operating point required by a mechanism.
Input → stages → output
Edit any value and the drivetrain, target, and motor curves update immediately.
Motor input
Gear stages
14.6667:1 totalMotion target and results
- Entered ratio
- 14.6667:1
- Predicted speed
- 301.91 rpm
- Speed vs. target
- +0.6%
- Efficient ratio
- 14.811:1
- Motor at target
- 4,443.36 rpm · 39.1 A
- Required power / motor
- 362 W · 76.9% peak
Drivetrain and Custom motor performance
RPM and torque through each shaft, followed by the interpreted motor curves.
Motor input
4,428.02 rpm
0.58 lbf·ft
Shaft 1
1,107.01 rpm
2.25 lbf·ft
Mechanism output
301.91 rpm
8 lbf·ft
Most efficient solution for the required power
The movement needs 341 W at the output. With 94.1% drivetrain efficiency, each motor must deliver 362 W at its shaft. The calculator selects the higher-efficiency of the two motor-curve points that produce this power.
- Motor speed
- 4,443.36 rpm · 74.1%
- Current per motor
- 39.1 A
- Motor efficiency
- 77.2% · 89% of max
- Required shaft power
- 362 W · 76.9% peak
- Ratio for desired speed
- 14.811:1
Estimated electrical input at this point is 469 W per motor · 469 W total at nominal voltage. This is the steady-state power for the entered speed and torque; acceleration requires additional power.
The curves are an engineering estimate, not a thermal or controller simulation. A breaker rating is not a motor-current cap; brief current can exceed that rating before a time-dependent trip. Battery or supply sag, configured controller limits, commutation, temperature, friction, and manufacturing variation change real performance.
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Quick answer
How this motor speed & torque calculator works
For a linear DC motor model, available torque decreases as speed rises from stall to free speed. Enter the motor endpoints and desired mechanism output to see the required power, current, efficient operating point, and gear reduction.
How to use the calculator
- 1Enter any motor’s voltage, free speed, free current, stall torque, and stall current from its published data.
- 2Set motor count and optional controller current limiting, then enter the desired output RPM and torque.
- 3Build the gear stages and efficiency that connect the motor to the mechanism.
- 4Compare the target and actual points on the torque, power, current, and efficiency curves before choosing a ratio.
Worked example
Half-speed motor operating point
- Inputs
- A motor with 6,000 rpm free speed and 3 N·m stall torque is evaluated at 3,000 rpm using the linear endpoint model.
- Result
- Modeled torque = 1.5 N·m and mechanical power ≈ 471 W.
At half free speed, the linear model produces half stall torque. Mechanical power is angular speed multiplied by torque.
Common questions
What to know before using the result
- Where is maximum power on a DC motor curve?
- In an ideal linear torque-speed model, maximum mechanical power occurs near half free speed and half stall torque. That high-current point is generally better suited to brief acceleration than continuous operation.
- Is the most efficient point the same as maximum power?
- No. Peak efficiency is normally at a higher speed and lower torque than peak power. The best operating point depends on the required power, cooling, duty cycle, current, and available gearing.
- Can I use a motor that is not in the FRC list?
- Yes. General mode is designed for any motor with published endpoint data. FRC mode only adds optional presets and purchasable gear references.
Formula
F = ma + Fᵣ · T = Fr · P = Fv · GR = ∏(N driven ÷ N driver)
Linear mode uses F = ma and drive radius; angular mode uses τ = Iα plus resisting torque. Multiply each gear-stage ratio for total reduction; required motor-shaft power also includes drivetrain losses.
Engineering references
Assumptions and limits
- Each listed row represents one external gear mesh between a driver and a driven gear.
- Gears on the same compound shaft rotate at the same speed and do not add another mesh.
- Torque excludes bearing, windage, lubrication, and other losses beyond the entered mesh efficiency.
- Required power is the steady-state power at the entered speed and torque; acceleration requires additional power and energy.
- Linear acceleration mode assumes constant acceleration from rest, constant drive radius, no wheel slip, and the entered resistance force. Its displayed power is the instantaneous mechanical output required at target speed.
- Angular acceleration mode assumes constant acceleration from rest, fixed rotational inertia, and the entered resisting torque.
- Motor curves are ideal constant-voltage approximations from entered or published free-speed, free-current, stall-torque, and stall-current endpoints.
- No current cap is applied by default. The optional cap represents a configured motor-controller setting, not a branch-breaker rating.
- Breaker trips are time- and temperature-dependent; battery sag, controller mode, current limiting, temperature, and manufacturing variation change real motor performance.
- Pitch, pressure angle, tooth form, center distance, and interference must be checked separately.
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